INSIVUMEH reported that on most days during 23-29 July the active lava dome of Santiaguito was visibly degassing and generating plumes, noting an ash explosion on 26 July rising up to 3 km (9,800 ft) a.s.l. that drifted W. On 28 July thin ash columns rose 3.2 km (10,500 ft) a.s.l. that drifted SW. On most days, fumarolic columns reached 2.7-2.8 km (8,800-9,200 ft) a.s.l. that drifted SW and weak to strong avalanches flowed towards Canyon Nima River I.

Geological Summary. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)